1. Field of the Invention
This invention concerns relief valves for placement in a fluid line to prevent cracking of the line when fluid therein freezes.
2. General Background
One of the most irritating aspects of cold weather is that exposed water pipes often freeze and crack. This cracking is caused by the expansion of water when it freezes to form ice. As the water expands within the confines of a water pipe, pressure builds within the pipe until it or associated structures rupture. Once ambient temperature rises to levels above freezing, the ice in the pipe melts yet a supply of running water to a building is not restored since the damaged pipe leaks.
It has previously been recognized that the internal pressure created by the freezing of water in the fluid line can be relieved by an inline pressure relief valve. U.S. Patents which have issued in this regard have been as follows:
U.S. Pat. Nos. 3,820,554; 2,205,463; 1,960,271; 1,876,938; 2,047,654; Great Britain Pat. No. 417; Canadian Pat. No. 447,072. These patents disclose pressure relief valves for fluid lines that open to release pressure at a preselected level. The prior art appreciates, that when water in a pipe freezes it freezes in those portions of the pipe adjacent the walls of the conduit. In other words, it has been found that water freezes in conduits from the outside of the interior, the water along the longitudinal axis of the conduit freezing last. However, the prior art fails to solve this problem.
The present invention recognizes this characteristic pattern of freezing in fluid lines and for the first time makes a successful attempt to solve this problem. The present inventors have accordingly provided a relief valve which projects into the fluid line being protected, and drains fluid out of the line from those portions of the line adjacent the conduit's longitudinal axis. This arrangement avoids the problems of the prior art in which previous relief valves were incapable of draining the fluid because they were situated adjacent the periphery of the conduit where water froze first. Placement of the relief valve adjacent the exterior of the conduit made it much more susceptible to being rendered inoperative by the water which froze initially near the walls of the conduit before the internal pressure in the conduit rose high enough to open the relief valve.